1. Field of the Invention
This invention relates to improvements in methods and apparatus for generating mechanical or electrical energy from solar energy, and, more particularly, to a method and apparatus for producing mechanical or electrical energy from solar energy directly from the thermally produced expansion of a fluid.
2. Description of the Prior Art
Recently, there has been renewed and vigorous efforts in harnessing or utilizing solar energy. This is particularly true in southwest regions of the United States in which the sun shines a large percentage of the days of the year, such as in New Mexico, Arizona and Nevada.
Aside from thermoelectric transducers, one of the classical methods for utilizing solar energy is by first converting the heat from the sun to mechanical energy, which can be easily converted to electrical energy for distribution and use. More particularly, many of the mechanical apparatuses used in collecting solar energy employ fields of pipes or other fluid containers. Most commonly, the fields employed have associated means for magnifying or focusing the sun's rays onto the field to elevate the temperature of the fluid in the field to a very high degree. Depending upon the particular fluid in the field, the fluid can be changed in state, for example, from liquid to gas, and the reconversion energy harnessed by way of, for example, a steam turbine or the like.
Other apparatus for utilizing the heat of the super heated water or fluid most commonly employ steam generators of one kind or another. For example, in Summers, The Conversion of Energy, Scientific American, September 1971, a system is described in which sunlight is impinged upon a collector panel to heat liquid sodium to a temperature of 1000.degree. Fahrenheit. The liquid sodium is conducted through a molten salt heat exchanger-reservoir to heat steam to drive a turbine. The molten salt is employed to hold the heat during the night and when the sun is hidden by the clouds so that steam will be produced nonetheless during those times. The turbine, in turn, drives a generator to produce electrical energy. The high temperatures involved are produced, in the field, naturally by some focusing or magnifying apparatus.
Among the difficulties encountered in the utilization of such solar energy conversion devices are the handling of the fluids and associated apparatus at such extremely high temperatures as are derived from the sun, not uncommonly in the neighborhood of 1000.degree. Fahrenheit, as above described. Much effort has been devoted, for example, just to the problems in containing fluids at such high temperatures and pressures within the field throughout their conversion to steam or other gaseous state. Furthermore, since the fluids are commonly changed in states, such as from liquid to gas, special condensers or other apparatuses are required to condense the steam or gas back to the liquid or fluid state after its energy has been removed, to continue the process. since many of the apparatuses advanced heretofore rely upon the heating of the fluid to produce steam or other gas directly or indirectly, they are operational only during the daytime, unless special heat retaining reservoirs are employed, such as that above described. This, of course, further complicates maintenance and increases the expense of the over-all system.
Another commonly used technique in efforts to achieve the most efficient use of the sun is by providing special apparatus to vary the alignment of the solar energy collector or field. Thus, the field in such instances is maintained at a particular attitude with respect to the sun so that the sun's rays fall thereon at a predetermined angle, ideally normal to the face of the field. Such alignment systems are particularly cumbersome, especially with relatively large collector fields, and, entail additional maintenance and expense.
Other, more direct systems which operate at lower temperatures and pressures have been proposed. For example, d'Amelio, The Hot-Water Thermal Cycle in the Utilization of Solar Energy, Solar Energy Journal, at page 138 et seq. describes apparatus in which the sun's energy is directed onto a flat plate collector field containing water. The water is heated to produce low pressure steam. The steam is then conducted to a turbine to turn it to generate mechanical rotational energy. The steam exiting from the turbine is then condensed in a condenser and recirculated via a pump back into the field.
The d'Amelio devices, however, present many of the problems mentioned above, but, in addition, do not operate in a continuous fluid state, in distinction to applicant's apparatus, as below described. On the contrary, the d'Amelio devices operate on the principle of a pressure difference developed across a turbine. This difference is developed by the pressure of the low pressure steam on the collector side of the turbine and by the lower pressure created by the condensation produced in the condenser on the other side of the turbine. Thus, some change in the state of the fluid is produced, even though it is at relatively low pressures and temperatures, to develop the necessary pressure differential to drive the turbine. Additionally, in the d'Amelio apparatuses, the collector field must be singularly oriented in a gravitional field to separate the non-vapor portions of the fluid to produce the pressure differential and to complete a continuous recirculating cycle.
The next step which might be suggested, although not actually disclosed by d'Amelio in the above referenced paper, is a continuous fluid system in which the fluid state is maintained throughout the system. Using the d'Amelio apparatus, this could utilize, for instance, the change in density of the fluid produced by the solar heating. This change in density could be applied to one arm of the turbine, and the fluid of unchanged density applied to another arm. The weight difference would produce a turning force upon the turbine which could be readily utilized.
This density difference possibility which might be envisioned (although not disclosed) should still be distinguished from applicant's apparatus which utilizes directly the produced fluid expansion, as below set forth.